Power transmitting apparatus



De'c. l, 1931. B. n. BEDFoRD 1,834,889

POWER TRANSMITTING APPARATUS Filed Aprilv 25, 1930 2 Sheets-Shet v1 W l um 1| v n ik |I| 23 Z4`k\m\ml;rz5 28 :s 26 V :4 /6 20 19 InventQP:

HisAttQPney.

Def.. 1, 1931. B, D BEDFORD 1,834,889

POWER TRANSMITTING APPARATUS Filed April 25, 1930 2 Sheets--Sheerl 2 Inventof: Burn ice Declford.

H i S Attorney Patented Dee. 1, 1931 v f UNITED *isf'ra'r-Esv Bunmcn n. BEDFonD, or soHnNncTADY, NEW YoRmAssiGNonj rrov GENERAL ELI-:orare coin/riparati', A CORPORATION or'y nrewpYoR-Kk rown'n TRANSMITTINQ AArrAnA'rUs n v nppiicatio'n filed April 25,

My invention relates to t-he transmission of electric power between direct and alternating current circuits or between alternating current circuits operated at different frequencies,

Different types ofapparatus have beeny provided in thev pastfor transmitting electric powerbetween direct and alternating current circuits. Someof these apparatus include a transformer and a pluralityo-f electric discharge paths or elements located either in the same device or in different devices. For satisfactory operation kof such yapparatus,itis essential'that means be provided for commutating the load current,i. e., shifting it from one discharge path toanother. The various means heretofore provided for this purpose have not been altogether satisfactory for the reason that deionization of the discharge path is in somecases not rapid enough to permit satisfactory `operation of the apparatus especially at high frequencies. Where the electric 'discharge ,path is through a vapor electric device provided with a grid or control electrode, rapid deionization of the discharge path maybe produced by subjecting the grid to a bias potential of large negative value.V The use of batteries for producing this negative grid biaspotential-is objectionable due to the expense and inconvenience Vof maintaining them inv suit- Y able' operating condition. In accordance with my invention, these difiicultiesare avoided by the provision .of an improved arrangement and method of operation whereby the desired negative bias ypotential is produced in respense to the ychange in the path `of the current transmittedthrough the apparatus.

My invention will-be better understood from the following description when consid- Vered kin connection with the accompanyingy drawings and its scope will be pointed out in the appended claims. Referring to the drawings, Fig. 1.- illus- Y trates an apparatus which embodiesmy in-` 1930. serial No. 447,406.

vention and is arranged to have its frequency determined by an external source of alter- ,nating currentrFig. 2 illustrates-a similar apparatus including means for controlling j its operating frequency; Fig.` 3 is a groupof curves relating to the operation of the apparatus illustrated by the previous figure;

vand Figs. 4 and 5 illustrate modifications of the apparatus shown in Figs. 1 and 2.Y

The apparatus of Fig. 1V includes a directcurrent circuit 10 and an alternating current circuit 11 which are interconnected through means including a winding12 and a pair of electric discharge devices 13 and 14 each provided-with a grid or control electrode for controlling the starting of current between its cathode and anode. Thus the device 13 is provided with a grid 15 arranged to control the current transmitted between its anode 16 fand cathode 17. and the device 14 is likewise provided with a grid 18 arranged to control Y the current transmitted between its anode 19 and cathode 20. The devices 13 and 14 are preferably of the vapor electric typey and may f be so designed that current between the anode andcathode starts when thegrid is subjected to 'zeropotentiah to a slight positive poten-A tial or to a potential of small negative value. Itis welluknown that the grid of such devices is effective to prevent starting of the current but is'usually incapableof interrupting this current after it has started.

f The winding 12 is provided with an intermediate terminal connected to one-of the .di-

rect-current leads 10 and with end terminals-1 connected to the anodes 16 and 19. Connected between the end terminals of the winding are three parallel circuits, one of whichis the alternating current circuit 11, another of which includes a capacitorQl, and the other" i of which includes a resistance elementQQ and V'grid 18. Potential for driving the 4applaratus or determining its operating frequency I14 rendering it conductive. vv'surned that the instant at which the device may be applied to the capacitance element 28 from a suitable source through a trans former 29. As hereinafter` explained, the characteristics of the apparatus are such. that a very small voltage applied to the capacitance element 28 is capable of controlling the operating frequency of lthe apparatus. In cases where the devices 13 and 14 require a positive grid potential in order to initiate a current in them, the secondary winding of the grid transformer 25 may be provided with an electrical midpoint and this point may be connected to the common cathode circuit ot the devices 13 and 14 through a resistor 2T whose resistance is preferably 4high enoufgli to limit any grid current flowing theretlfnough to a negligible value.

In explaining the operation Aof the above described apparatus, it will be lassumed that one of the devices, for example the device 13, is initially rendered conductive. Current will now flow as shown by the arrows of Fig. 1, the solid line arrows indicating the total current including magnetizing current and the dotted line arrows indicating load current and capacitor current. As will be well understood by those skilled' in the art, the capacitors 2l and 23 become charged to substantially twice the poten-tial of the direct currentcircuit. After these capacitors become substantially completely charged, it will be assumed that the potential applied to the capacitor 28 by means of the grid transformer 29 will reverse the control potential and apply a positive potential to the grid of the device It will be as- 14 is rendered conductive corresponds to the time t1 of Fig. 3 in which the curves Eu, Ig, and Eg, indicate the anode voltage, the grid current, and the grid voltage, respectively, of the device 13. As is well understood by those skilled in the art, when the device 14 becomes conductive the cathode lof the device 13 is made negative with respect to its anode by approximately twice the potential of the direct current circuit due to the fact that the potential across the capacitor 21 cannot change instantaneously. This results in the interruption of current in the device 13 and its establishment in the device 14. The capacitor 21 now rapidly discharges, aiding in the reversal of the magnetizing current of the winding 12, so that the anode potential of the device 13 increases positively at a very rapid rate represented by the initial portion of the curve Ea between intervals t1 and t2 of Fig. 3.v During this commutating period., that is, the interval during which the anode potential of the device 13 is negative, the capacitor 23 also tends to discharge but, due to the impedance of the resistor 22 and the grid transformer 25 in its discharge path, its discharge takes place at a very much lower rate. It is seen that the difference in potential between the capacitors 21 and 23 is impressed directly on the resistor 22 which excites the grid transformer 25. In other words, as soon as the device 14 becomes conductive and during the commutating period, the grid of the device 13 in which current has just been interrupted is subjected to a very Ahigh negative potential transient. As the potential drop in the device 14 is very low and due to the fact that the impedance of the resistor 27 is suiiiciently high that it may be neglected in ordinary operation of the apparatus, the full potential of the secondary winding of grid transformer 25 is impressed upon the grid of the device 13 rather than a half of the potential of the secondary winding as is ordinarily the case with apparatus of this type. It will be noted also that, due to the high impedance of the resistor 27, the only path for the grid current of the device 14 includes the grid-cathode circuit of the device 13. Since grid current flows in the device 13 only during the period of deionization, the positive grid current of the device 14 is limited in magnitude and duraytion to the ion cleanup current of the device 13 so that any danger of damage to the grid of the device 14 by excessive grid current is avoided. Capacitors 21 and 23 now become charged to an opposite polarity. The poten! of a magnitude only suflicient to render the devices 13 and 14 conductive during their respective half cycles of positive grid potential and that the negative potential required for deionization of the device in which current has just been interrupted is supplied byV means of the transformer 25 in the manner described above.

Danger' of damaging the grids by excessive current is avoided because the grids draw current onlyduring commutation, the ion` clean-up of one device being exactly balanced by the electron current of the other device if the resistance 27 is made infinite. With very little grid power input from the transformer 29, deionization equal to that secured with a high voltage grid bias battery is obtained and the load capacity of the apparatus is greatly increased. The application of the alternating driving voltage to the capacitor 23 has the advantage that it per-"'- niits rapid deionization and does not load the excitation circuit. Due to rapid deionization, the operation of the apparatus at low frequencies is improved and the rangel of operating frequencies is greatly extended.

' 'igea-1.889

The apparatus illustrated by Fig. 2 is similar in many respects to that of' Fig. `1 but -diii'ers therefrom in that it supplies its own excitation or isl self-driven. Y capacitor kand an adjustable' resistor .31

It includes a which are common to the gridcircuits of the devices 13 and 14and are connected in parj allel withone another.

The excitation circuit including the ca`` pacitor '30 and resistance 31 operates in a manner similar to theexcitation circuit of Fig. 1. Change in operating frequency is produced by adjustment of the resistance 31, the frequency of oscillation being largely determined by the rate at which the capacitor 30 `discharges through the resistance `31. This frequency, however, is dependent to some extent on the magnitude of the load `to which the apparatus is subjected for the reason that the chargel of the capacitor 30 is dependent on thevoltage of the load 11, the transformer ratio, the' sizeof the Vcondenser'23, and the size of the resistances 22 and 27; Where the alternating current load 11 is asynchronous motor, it has been found that a range of speed variation between 500 and 4000 R. P. AM. may be readily secured. A marked advantage of the apparatus of Fig. 2 is that it functions as analternating sourcel ofvariable frequency and maybe readily utilized to energize alternating load circuits located in districts where only dif rect current isavailable.

riss

In the case of some tubes whichV require a positive grid voltage tostart in operation, it. may be desirable to connect one side of the resistor 31, as indicated in Fig. 2, to the positive direct current line instead of the negative. This arrangement is indicated in Fin. 4. This maybe desirable in cases where tle mere discharging of the negatively discharged condenser to zero will not be suincient to start the tubes into operation.

In the arrangement shown in Figs. 1 and 2, a capacitor and resistor are connected in series, the voltage across the resistor being impressed on the grids of the tubes. Similar results can be obtained by the use of a series inductance andresistor 32, as shown inFig. 4, and by impressing the voltage'across the inductance'upon thev grids of the tubes, the

y inductance in this case constituting the priother appears largelyacross the reactor denser 23 and inductance 33 and resistance 34 are connected in series and the variable resistance is connected in shunt to 33 and 34.1 The potentiometer 36 connected across the directcurrent circuitwill supplyfpositive ,1,

grid excitation quire it. f i In each'of the connectionsV which I have shown the polarity `of the grid transformers Vto such tubes as may'revshould be such that when onevend of theprimary is positive with respect to the other end, the corresponding endrof the secondary will be negative with respect to the other end. What I claim as new and desire'to secure by Letters Patent of the United ,States is:

' 1. The combination of a pair of electric discharge devices each provided with a grid for controlling the starting of current b etween itscatliode andV anode, awinding connected between the anodes of said" devices"-vv`x and provided with an intermediateterminal, a direct current circuit connected between said terminal and the catliodes of said devices, a capacitor connected between the anodes of said devices, capacitor and resisti' vance elements connected between said anodes in series with one another, and means for subjecting said grids to potentials dependent on the voltage drop of said resistor. j I

2. n The combination of a pair of electric discharge devices each provided with a grid for controlling the starting of current between its cathode and anode, a winding connected between the anodes of said devices and provided with an intermediate terminal, adirect current circuit connect-edA between'said terminal and the cathodes of said devices, a capacitor connected between the anodes' of said devices,capacitor 'and resistance elements connected between said aiiodes in series with one another, means'for subjecting said grids topotentials dependent on the voltage of said resistor, and a resistance-element'common 'to the grid circuits of-said devices.

y3. The combination of a pair of electric discharge devices each provided with agrid for controlling the starting of current between vits cathode and anode, a .winding connected between the anodes of said devices and provided with an intermediate terminal, a dir rect current circuit connected between said terminal and the cathodes of said devices, a capacitor connected between the anodesof said devices, a plurality of impedance means vconnected between'said anodes in series with oneanother, means for subjecting said grids to potentials'dependent on the voltage drop ofone of said impedance means, and an impedance elementcommon to the grid circuits ofjsaiddevices.

' 4. The combination ofa pair'of electric `discharge devices each provided witha grid for Vcontrolling 'thestarting of current between its cathode and anode, a winding connected between the anodes of ksaid devices .its

and provided with an intermediate terminal, a direct current circuit connected between said terminal and the cathodes ot' said devices, a capacitor connected between the auodes of said devi-ces, a plurality of impedance means connected between said anodes in series with one another, means for subjecting said grids to potentials dependent on the voltage drop of one of said impedance means, an impedance element common to the grid circuits of said devices, and frequency control common to said grid circuits.

The combination of a pair of electric discharge devices each provided with a grid for controlling the starting of current between its cathode and anode, a winding connected between the anodes of said devices and provided with an intermediate terminal, a direct current circuit connected be-tween said terminal and the cathodes of said devices, a capacitor connected between the anodes of said devices, capacitance and resistance elements connected. between said anodes in series with one another, means for subjectingY said grids to the potential across said resistor, and means common to said grid circuits for controlling the frequency at which current is transferred from one to another ot said devices.

6. The combination of a pair of electric discharge devices each provided with a gri-d for controlling the starting of current between its cathode and anode, a winding cennected between the anodes of said devices and provided with an intermediate terminal, a direct current circuit connected between said terminal and the cathodes ot said devices, a capacitor connected between the anodes of said devices, capacitance and resistance elements arranged to subject the grid circuits of said devices to potentials dependent on the voltage ot' said windings, and means including capacitance and resistance elements common to said grid circuits for controlling the Jfrequency at which current is `transferred from one to another of said devices.

7. Apparatus for transmitting energy from a direct current supply circuit to an alterhating current load circuit comprising an inductive winding, means for interconnecting the circuits through said winding including a pair of electric discharge devices ach provided with a control grid. means associated with said discharge devices for commutating the current therebetween. and means for exciting said grids to successively render said discharge devices alternately cond'uctive'afnd nonconductive and for accelerating thc deionization of said discharge devices during the commutating period.

8. Apparatus for transmitting energy from a direct current supply circuit to an alternating current load circuit comprising an inductive winding, means for interconnecting the circuits throughY said winding including a pair of electric discharge devices each provided with a control grid, means associated with said discharge devices for commutating the current therebetween, and .means for exciting said grids to successively render said discharge devices alternately conductive and non-conductive and for unpressing a transient of negative potential on each control grid immediately after current has been interrupted in its associated device.

9. Apparatus for transmitting energy from a direct current supply circuit to an alternating current load circuit comprisingan inductive winding, means for inter-connect` ing the circuits through said winding including a pair of electric discharge devices each provided with a control grid, means including a capacitor associated with said discharge devices for commutating the cur- Y rent therebetween, means for exciting said vgrids to successively render said discharge devices alternately conductive and non-conductive, and means responsive to the discharge of said capacitor during the com# 

